1. Field
Embodiments are related to a nano-color coating technology which uses an optical absorption due to a localized surface plasmon resonance occurring at metal nanoparticles as a coloring mechanism, and more particularly, to a nano-color coating technique for greatly enhancing an optical absorbance due to a localized surface plasmon resonance by employing a resonant structure composed of a composite layer, where metal nanoparticle layers and matrix layers are alternately arranged, and a bottom mirror layer, and also for greatly enhancing the absorption band shift just by controlling a nominal thickness of the metal nanoparticle layer and a separation between the particle layers, and to a method for fabricating the same.
2. Description of the Related Art
A color coating technology for providing a color to a base body is applied to a great variety of technical fields including not only traditional decorative coating but also display color filters, security labels, selective optical absorption layers, tunable optical filters, colorimetric sensors or the like. For such applications, there is a need for an eco-friendly color coating technology which is based on a thin coating layer but ensures excellent color tunability and high chroma in spite of using a relatively simple process and materials combination.
In a traditional wet-coating process using a paint, a coating layer is demanded to have a thickness of at least several tens or hundreds of microns in order to realize a clear color of high Chroma due to the characteristic of an organic dye and is also vulnerable to heat and ultraviolet light. In addition, due to its process nature, it is difficult to entirely exclude hazardous substances harmful against the human body, and thus not eco-friendly.
Meanwhile, a color coating technology using a dry deposition process has advantages that it is eco-friendly and can be adopted to a batch process for manufacturing various opto-electronic materials/devices. Typical ways of coloring are using optical interference effects arising from a periodic multilayer film composed of dielectric layers with different refractive indices, or a Fabry-Perot etalon in which a dielectric layer is sandwiched between two metal films. These coloring methods based on optical interference effect can be disadvantageous in that they basically demand a minimum thickness of the order of the light wavelength and cause a color difference depending on observation angles.
Besides the interference coloring, a simple color coating based on a metal film such as Zr, Ti, Cr, Nb or the like or nitride films of Ti—N system is also widely used for exterior coating of consumer electronics or decorative coating because it can produce several metallic colors such as gold, blue, wine or the like. However, this is not suitable for a current trend towards elegant IT product design since it appears to lack premium feel of metallic sheen and has limitation in the achievable range of colors.
Recently, a new-concept color coating technology using a physical effect pigment is spotlighted as an alternative. In particular, a localized surface plasmon resonance phenomenon occurring at nano-sized metal particles dispersed in optically transparent dielectrics or polymer matrix shows very strong optical absorption spectra in a specific visible wavelength range and thus has been recognized as a promising colorant. The plasmonic nanoparticles not only show a molar extinction coefficient of about 105 times larger than that of a general organic dye but also have the advantages of tuning the surface plasmon resonance wavelength in a wide range by means of the metal species, shape and size of particles, and a combination with a matrix.
However, the plasmonic nano-color coating fabricated by a vacuum deposition process does not generally generate a vivid color with a sufficiently high chroma. A conventional method for enhancing the chroma is to increase a volume fraction of metal nanoparticles to cause sufficient optical absorption or to increase a total thickness of the sample. Such approaches, however, may increase the consumption of precious metal suitable for exciting surface plasmon or give rise to an undesirable interference color due to the increased total thickness of the coloring layer. In addition, since the control of shape and size of particles are highly restricted in the deposition process, in order to realize diverse colors, the combination of metal and matrix should be frequently changed, inconveniently. Therefore, there is a demand for a method for greatly improving a color chroma and hue angle control range while maintaining the materials combination and the total thickness of color coating below a certain extent.
Another previous plasmonic nano-color coating technology employed a Fabry-Perot type resonator structure consisted of a metallic mirror, transparent resonance interlayer, and a metal nanoparticle layer, which made it possible to obtain a relatively clear color of high chroma. However, since the coloring mechanism is still based on the interference effect, the change of color is dominated by the thickness of the dielectric resonance layer, thereby exhibiting interference color attributes.